Exhaust gas generated by combustion of fossil fuels in furnaces, ovens, and engines, for example, contains nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). Vehicles, e.g., diesel vehicles, utilize various pollution-control after treatment devices such as, for example, a NOx absorber or Selective Catalytic Converter (SCR), to reduce NOx. For diesel vehicles using SCR, the NOx reduction can be accomplished by using ammonia gas (NT3). In order for SCR catalyst to work efficiently, and to avoid pollution breakthrough, an effective feedback control loop is needed. To develop such control technology, there is an ongoing need for economically-produced and reliable commercial ammonia sensors.